A cable network typically includes at least one headend system that services a plurality of subscriber devices. Generally, the headend system is stored within a central office of a cable service provider and includes one or more cable modem termination systems (CMTSs) and conditional access servers (CASs) that access a backbone network (such as the Internet). Each of the CMTSs and CASs may service customer premise equipment (CPE), such as cable modems (CMs) and set-top boxes (STBs). Traditionally, the cable network includes coaxial cable that is laid up to and installed inside a subscriber's premises to couple the CMTSs and CASs of the headend system to the CPE (which may also be referred to as “subscriber devices”). Over this coaxial cable the CMTSs, CASs, and subscriber devices communicate via radio frequency (RF) signals, which consists of modulated analog and digital signals.
While coaxial cable provides sufficient bandwidth to transmit television and low-speed Internet services, the recent growth of the Internet and desire to provide high-speed Internet access via the cable network has begun to generate new bandwidth concerns. In response to these concerns, most cable service providers have upgraded links coupling the headend system to the backbone network from coaxial cable to higher bandwidth fiber optical cable to facilitate higher bandwidth access to the backbone network, creating what may be referred to as a “hybrid fiber coaxial network” or “HFC network.”
Some cable service providers also have begun to upgrade the coaxial cable extending from the CMTSs and/or CASs to the subscriber premises but most have not, as of yet, extended the fiber optical cable all the way, or the “last mile,” to the subscriber's premises. Recently, cable service providers have begun to consider upgrading this last mile to fiber optic cable to offer a service known as fiber-to-the-home (FTTH) or fiber to the premises (FTTP). In this all-fiber network, all communications typically occur via a baseband digital protocol, such as the gigabyte passive optical network (GPON).
Although all-fiber networks may offer relatively higher transmission speeds and bandwidth when compared to HFC networks, upgrading to an all-fiber network may require large upfront expenditures. To support communications via baseband digital protocols, upgrading the last mile may require replacing not only the coaxial cable to the customer premises but also the CMTSs, CASs, any CPE or subscriber devices, and the coaxial cable installed within the subscriber's premises. As a result, an intermediate upgrade strategy has been proposed where RF signals are converted at the headend to optical signals and transmitted over fiber optic links, which are made of glass and cannot directly transport electrical signals. The electrical signals from the subscriber equipment may be used to modulate light generating devices, such as lasers, thereby converting the RF signal to an optical signal. Using RF-modulated light allows fiber optic cables to carry the same RF signals as coaxial cable. At the CPE or subscriber devices, the optical signals may be converted back to RF signals, e.g., using a photodiode. The resulting network may be referred to as an RF Over Glass (RFOG) network.
As an RFOG network simply converts the RF signals to a form that can be transported over optical fiber and converted back to RF at the central office, the cable service provider can continue to use his RF infrastructure at the central office and the home. The cable service provider does not need to upgrade the CMTS, CASs, CPE or subscriber devices, and coaxial cable located within the subscriber's premises, thereby substantially reducing upfront costs required when compared to upgrading directly to the all-fiber network. Instead, the cable service provider may lay fiber optic cable to the subscriber's premises, implement the required electrical-to-optical (E-to-O) and optical-to-electrical (O-to-E) converters at the ends of the fiber optic cable, and at some later time, when the service provider has sufficient capital, convert the RFOG network to a dedicated optical network that communicates using a baseband digital protocol, such as a GPON, active Ethernet or other optical network transport.